The invention relates to an electro-therapeutic device for the treatment of the preferably human body with electrical currents having a defined frequency and amplitude. The device comprises at least two flat electrodes that can be connected with the body to be treated, for closing a current circuit via said body, in connection with which a treatment current, the amplitude (A) and frequency (f) of which can be simultaneously modulated, can be introduced into the body to be treated.
Such a device is known already from the Japanese patent application JP 5-212 126 A.
A similar device, which, however, is operated without simultaneous modulation of the amplitude and frequency, is known from the European patent specification EP 0 659 099 B1.
A distinction is made in connection with this known electro-therapeutic device between two methods of application of stimulation current:                the “polar stimulation principle” that is depending on the polarity; and        the “non-polar stimulation principle that is independent of the polarity.        
The polarity stimulation principle is applicable to low-frequency currents in the range of from 0 to 200 Hz, and the non-polar stimulation principle is applicable to so-called medium-frequency currents in the range of from about 1 to 100 kHz.
Furthermore, in the field of electro-therapy, a distinction can be made between stimulation effects that depend on the frequency, and stimulation effects that are independent of the frequency. Furthermore, methods are known that elevate these effects in an isolated manner and combine them with each other in a useful manner.
In connection with the methods depending on the frequency, the frequency of the treatment current is varied, and the amplitude of the treatment current is varied in connection with the methods depending on the amplitude.
If, in a double-logarithmic system of coordinates, the thresholds of the frequency are represented as a function of the frequency, whereby the intensity of the voltage or current are represented as ordinate values and the frequencies as abscissa values, the result is an approximately straight-line development of the curve. However, the developing curve is ascending in an approximately straight-lined manner only because the intensity threshold values rise to a relatively higher degree as the frequency values are rising, so that the ascent of the curve grows to a minor extent with the increase in the frequency accordingly. Expressed in other words, the approximately straight-lined curve “is sagging through a little”.
The aforementioned, only approximately straight-lined development of the curve represents the stimulation threshold, thus -a frequency-dependent intensity threshold value that is triggering action potentials when it is exceeded.
The frequency at which this threshold is repeatedly exceeded due to repeated variation of the amplitude, determines the frequency at which the above-mentioned action potentials are triggered in conjunction with the stimulation method depending on the amplitude.
In the aforementioned system of coordinates, the treatment currents applied in the field of electro-therapy depending on the frequency are flowing in a horizontal straight line, and the treatment current generated in the case of the treatment depending on the amplitude are flowing on a vertical straight line.
The two methods are accordingly referred to also the horizontal and the vertical stimulation.
Purely below-threshold applications are known in connection with both methods are well if, in the therapy, importance is attributed to effects other than the described stimulation effects.
The successes achieved in electro-therapy primarily relate to the areas of alleviating pain, the stimulation of cross-striated and smooth musculature, of influencing the blood circulation and the metabolism; inhibition of inflammation, and promotion of the regeneration in the area of healing wounds and bones.
The basis for the therapeutic spectrum of currents are their physical parameters and the influences that are derived from these parameters and are acting on the functions of the structures of the biological systems being treated.
Such parameters of the current are most of all the frequency with its modulations; the modulation frequencies; and the intensity parameters such as the voltage, the current intensity, the output; the locally effective field strength; the current density, the output density etc., as well as in turn their modulation as the amplitude modulation at the amplitude modulation frequency and the degree of modulation.
In connection with currents, a distinction has to be made between systemic and local compatibility, as it has to be made in connection with pharmaceuticals.
The systemic compatibility of currents is determined most of all by the electro-toxic dosage required for triggering cardiac ventricular fibrillation, or for triggering epileptic attacks.
The “poorest” local compatibility is exhibited by direct current because of the risk of causing local burns and cauterization. Low-frequency currents are quite incompatible as well because of the poor manner in which they can be inroduced into the body transcutaneously, and the low local pain thresholds deriving therefrom. Furthermore, in most cases, low-frequency currents also comprise a direct-current component with the problems mentioned above.
The disadvantages of low-frequency currents and of direct current can be avoided in connection with the so-called “horizontal stimulation” in the intermediate frequency range between 1 kHz and 100 kHz according to the device known already from EP 0 659 099 B1. The principle consists in that in the system of coordinates mentioned above, a horizontal low-frequency change in the carrier frequency takes place in such a manner that a variation is effected between an above-threshold and a below-threshold carrier frequency range, i.e. the medium-frequency carrier frequencies are frequency-modulated at a low frequency.
In this connection, the method of horizontal stimulation is not free of drawbacks either. In order to reach the threshold of a group of sensitive motor or sympathetic nerve fibers, the intensities are raised to the same extent between an upper and a lower corner frequency. The threshold of a nerve fiber is first exceeded in this connection with the lower corner frequency. After the threshold has been reached, the duration of the above-threshold state in the range of the lower carrier frequencies is still short as compared to the below-threshold state in the range of the higher carrier frequencies.
If the number of nerve fibers stimulated above the threshold is to be increased in order to raise, for example the intensity of the muscular contraction via a greater number of stimulated motor nerve fibers, or via a greater number of sensitive sympathetic fibers, or for the purpose of amplifying the intensity of the counter-irritation for the alleviation of pain, or for the purpose of intensifying peripheral effects of vasoconstriction via a greater number of sympathetic fibers, the duration of the above-threshold state is prolonged for the fibers whose threshold have been exceeded first, and the duration of the below-intensity state is reduced, and if the intensity is raised further, even the entire modulation period may be in the above-threshold range.
A continually growing number of nerve fibers are in fact stimulated above the threshold with each increase in the intensity; however, the “above-the-threshold” time increases at the same time for the fibers already stimulated above the threshold, so that due to the omission of interruption via the generation of volatile excitomotor activity, a permanent polarization with corresponding blocking may finally entail.
For a major part of the fibers, the modulation of the frequency therefore still takes place only in the above-threshold range.
In that case, the desired range of stimulation that is synchronous with the stimulation frequency is vacated and the range of the volatile excitomotor activity is entered into instead, without any clear relation to the stimulation frequency and discharge frequency of the stimulated structure in terms of time. Finally, the risk is posed that a permanent polarization of the cells is caused, i.e. of the nerves or muscles that actually should have been stimulated. In connection with nerves, the local permanent polarization leads to line blockage, and in connection with muscles to a reversible physiological contraction.
For these reasons, it is not possible according to the method of horizontal stimulation to generate maximal tetanic contractions, as it is possible by means of vertical stimulation.
According to EP 0 659 099, a further field of application of horizontal stimulation consists in the generation of so-called interferences. In this connection, two medium-frequency currents that have only minor frequency deviations among each other, are superimposed for generating low-frequency interference currents. An amplitude modulation ensues in the field of superimposition of the medium-frequency currents mentioned above. The modulation of the amplitude is caused by the difference in the frequency of the two medium-frequency currents supplied. The aim of such a superimposition of two or more current circuits is to raise the intensity of the treatment by adding up the individual intensities, so that action potentials or heat are generated in this range.
In this connection, a distinction can be made between phases of the pure heat treatment, and of the heat treatment with action potentials and treatment pauses, by controlling the method accordingly.
During the treatment pauses, in which neither heat nor action potentials are generated, a non-stimulatory metabolism effect remains that is referred to as the so-called “green metabolic effect”. This designation is to be understood as being the delimitation vis-à-vis the “yellow stimulation effect”, in connection with which the groups of nerves are stimulated in a targeted and stimulating manner.
In the interference therapy, the current circuits are applied by means of the respective electrodes in such a manner that the field of superimposition develops in the respective region of treatment.
A further drawback of the device already known from EP 0 659 099 consists in that relative long pauses of the sensitive perception are unavoidable in connection with the so-called slow horizontal frequency modulation. Only “green metabolic effects” are expected during these pauses; however, these effects could be exploited in a more efficient manner with an amplitude that is higher than the one usually applied in connection with this method.
In addition to the prior art described in the foregoing, devices have become available in the market in the meantime in conjunction with which it is possible to select between methods of the vertical and methods of the horizontal stimulation. This younger generation of devices is therefore adapted to carrying out both methods alternatively.
The invention is based on the problem of providing an electro-therapeutic device that avoids the drawbacks of the prior art and offers a constant level of the safety standard in conjunction with increased treatment comfort and an expanded field of application.
The object constituting the basis of the invention is resolved by an electro-therapeutic device according to the features of the invention. Advantageous further developments of the invention are also specified.
Owing to the fact that according to the invention, a treatment current is generated that is simultaneously amplitude- and frequency-modulated within a medium-frequency range of from 1 to 100 kHz, and that this current is introduced into the body to be treated, the benefits and possibilities of horizontal and vertical stimulation are united in one single method, on the one hand, and, furthermore, the shortcomings that are necessarily inherent to these methods are avoided on the other.